The present invention relates to a hydraulic or pneumatic device which exhibits a high reliability over an extended period of time.
The hydraulic tube for power transmission for general industrial use and the pneumatic tube for automobile air brake have heretofore been made of a material such as metal, rubber and resin. However, a tube made of a resin having a lighter weight and a good workability (mountability) has recently been used more and more.
As the material of the resin tube there has been widely used a plasticized flexible material such as nylon 6, nylon 11, nylon 12 and copolymer comprising these nylons as main components from the standpoint of low temperature impact resistance, stress cracking resistance by metal chloride and flexibility.
A handbook of nylon resins describes that nylon 11 and nylon 12 comprise a higher alcohol, hydroxybenzoic acid ester, aromatic sulfonamide, etc. incorporated therein as a plasticizer. Among these nylons, nylons plasticized with an aromatic sulfonamide are normally used.
However, a pneumatic or hydraulic tube made of such an ordinary commercial flexible nylon plasticized by an aromatic sulfonamide-based plasticizer can have an impaired airtightness after a prolonged use. This is because when the tube is exposed to a relatively high temperature, the plasticizer bleeds out to reduce the thickness of the tube, giving an adverse effect, or when an O-ring or the like mainly composed of a polar rubber, in particular NBR, which is normally used, is used as a seal, the plasticizer which then bleeds therefrom and is entrained by air or is extracted with an oil is then absorbed by the sealing material to swell the rubber, deteriorating the sealing properties thereof and hence the airtightness of the tube.